Modification of Hoek-Brown Strength Criterion Based on Cumulative Damage of Blasting

The traditional classification method of tunnel surrounding rock does not take into account the effect of blasting damage factors on the surrounding rock classification. As the primary excavation method, the effect of blasting damage on the rock classification criteria cannot be ignored. The calculation method of mechanical parameters of rock mass is discussed based on Hoek-Brown strength criterion. Then, the deficiencies in determining the material parameters in the Hoek-Brown strength criterion and related improved formulas are elaborated and clarified. Considering the cumulative damage effect of blasting, the calculation method of Hoek-Brown empirical constants m_b, s, a for different rock levels is proposed, and the formula of Hoek-Brown strength criterion empirical constants for different rock levels considering the tunnel burial depth and blasting cumulative damage effect is established. Moreover, the accuracy of the Hoek-Brown strength criterion rock empirical constant correction formula is verified by testing the correction formula with the acoustic variation rate obtained from the blasting field test in Longnan Tunnel No. 1 inclined shaft.